Aaaagh!
You seem to have been hit by the dreaded Cryptolocker:
http://www.bbc.co.uk/news/technology-25506020
To the best of my knowledge, nobody has found a cure for it yet (and many people have reported that paying the ransom money hasn't resulted in the problem being fixed either). Sorry!
You'll probably need to get the laptop's hard drive completely wiped and then reinstall Windows, all of your drivers and all of the software but, regrettably, files such as documents and pictures will be lost forever.
For
future reference (as it will be absolutely no use to you at the moment) please read this:
http://www.theguardian.com/money/2013/oct/19/10-ways-beat-cryptolocker-protect-files
The most important bit is, of course, where it says that up should BACK UP all of your files onto external media. Even without the problems caused by cyber-criminals, hard drives will fail and people will lose vital data.